Mango Pests And Diseases

Description

Mango Pests And Diseases

The commonest and most troublesome enemy of the mango in tropical America is anthracnose. This is a parasitic fungus (Colletotrichum gloeosporioides Penz.) which attacks many different plants, and is particularly known as the cause of wither-tip in citrus fruits. It is a species of wide distribution which springs up with no evident center of infection whenever the weather is warm and moist. On the flowers and flower-stalks of the mango it appears in the form of small blackish spots. Often it causes many of the flowers to drop. On the leaves, spots and sometimes holes are produced; these begin as minute black dots and enlarge until they are about an eighth of an inch in diameter. Young fruits may be attacked and made to drop in large numbers, while older fruits become spotted with black or streaked, and their keeping qualities are impaired.

S. M. McMurran, who studied anthracnose control methods in Florida and reported his results in Bulletin 52 of the United States Department of Agriculture, says:

"Spraying before the buds begin to grow is of no value so far as protecting the inflorescence, and later the young fruit, is concerned. These must be kept covered with the fungicide (Bordeaux mixture) while growing, if fungous invasion is to be prevented. The difficulty of so protecting the inflorescence is at once apparent. Elongations of the panicle continue for a period ranging from 10 to 15 days. Those which were sprayed every third day were practically all disease-free when the flowers began to open. This, however, required four sprayings in one case and six in the other. Those sprayed every fourth day showed but little more disease than those sprayed every third day, but those on which the spray was applied at five and six day intervals had traces of disease, showing that they were less perfectly protected.

"The spraying of the inflorescence at least three times, beginning when the buds are just swelling and repeated every fourth day until the flowers open, will help to prevent the dropping of fruit caused by the disease on the peduncles and pedicels.

"The inflorescence may be kept in a clean condition up to the time of blooming; but, when this takes place, immediately there are hundreds of points which are not covered by the fungicide and are open to infection . . . spraying is of little or no value in controlling the blossom blight form of the disease, and profitable sets of fruit can be expected only during seasons which are dry at blooming time, unless varieties which are resistant to the disease are developed and cultivated."

This disease is a serious obstacle to the production of marketable mangos in the West Indies. J. B. Rorer,1 who conducted spraying experiments in Trinidad, found, however, that "All of the sprayed trees set more fruit than the control trees, and the greater part of the fruit ripened without infection, while the fruit on unsprayed trees was for the greater part spotted or tear-streaked. The fruit from sprayed trees matured a little later than that from the unsprayed and was somewhat larger in size. The foliage of sprayed trees was much heavier than that of the unsprayed." If fruit is not sprayed to keep it clean while it is developing, it not only is less attractive when placed on the market, but is subject to decay.

Anthracnose does not appear to be mentioned by Indian writers on mango culture. It is known, however, to be serious in Hawaii as well as in tropical America. Bordeaux mixture used in its control can be made according either to the 4-6-50 or the 5-5-50 formula, using a small amount of whale-oil soap to make it adhere more tenaciously to the foliage.

Ethel M. Doidge, in the Annals of Applied Biology (1915) describes a disfiguring and rotting disease of mangos which occurs in South Africa. It is caused by Bacillus mangiferoe, an organism which is carried by water or may be transported from tree to tree by the wind. Woody tissues are not affected, but small angular water-soaked areas appear on leaves, longitudinal cracks are produced on petioles, and discolored spots on twigs and branches; while on the fruit the first sign of the disease is a small discolored spot. This spreads, becoming intersected with cracks, and may extend some distance into the flesh. No means of controlling this bacterial disease has yet been discovered.

1 Trinidad and Tobago Bull. 5, 1915.

Of the insects which attack the mango, the fruit-flies (Trype-tidae) rank first in importance. Belonging to this family are the Mediterranean fruit-fly (Ceratitis capitata Wiedemann), which has become a very serious pest in Hawaii and several other regions; the Queensland fruit-fly (Batrocera tryoni Froggatt), distributed throughout Malaysia and Australia; the mango fruit-fly (Dacus ferrugineus Fabricius), which occurs from India to the Philippines; the Mexican fruit-fly (Anas-trepha ludens Loew); and Anastrepha fraterculus Wiedemann, another Mexican species, now distributed throughout Central and South America and the West Indies. Several other species have also been reported as attacking the mango. The females of these flies insert their eggs beneath the skin or in the flesh of the fruit, and the larvae render it unfit for human consumption. Control is difficult; the sweetened arsenical sprays have met with varied success, and control by means of parasites is receiving attention.

In some parts of India the mango hopper (various species of Idiocerus) is troublesome. H. Maxwell-Lefroy 1 writes:

"These insects resemble the Cicadas superficially but are much smaller, being one-sixth of an inch in length. They are somewhat wedge-shaped with wings sloped at an angle over the back. Large numbers are found on the mango trees throughout the hot weather but especially at the flowering season when there is a flow of sap to the flowering shoots. These insects pass through their active life on the tree, sucking the juice of the soft shoots and causing them to wither. . . . There is only one effective treatment which must be adopted vigorously. This is spraying with strong contact poison such as crude oil emulsion or sanitary fluid."

1 Indian Insect Pests.

Another serious pest in India is the mango weevil (Sternoche-tus mangiferoe Fabricius, better known as Cryptorhynchus mangiferce). It is not limited to India, but is found also in the Straits Settlements, the Philippines, South Africa, and Hawaii. In the last-named country it has become formidable. "The insect is a short, thick-set weevil, dark brown in color, one-third of an inch in length. . . . The grubs bore in the kernels of the mango fruit when it is growing large; these grubs pupate inside the fruit and as the mango ripens become beetles, eating their way out through the pulp of the fruit, which they spoil." Maxwell-Lefroy recommends that all infested fruits be destroyed, and that weevils hiding in the bark of the tree be killed in August. Kerosene emulsion is useful in destroying those which are on the bark. It is also advisable to cultivate or flood the ground beneath the trees, in order to kill weevils which may be lurking there.

In Florida, red-spiders and thrips are responsible for extensive injury to foliage, leading to disturbances of the general health of the trees; but contact sprays, e.g., lime-sulfur or nicotine, properly applied, will effect complete eradication.

The mango bark-borer (Plocoederus ruficornis Newman) is a formidable enemy of the mango in the Philippines. This is a large beetle. C. R. Jones 1 says of it:

"The mango bark borer, while a comparatively unknown pest outside the vicinity of Manila, is exceedingly dangerous, largely on account of its feeding habits, which make detection difficult. The beetle has, so far as we know, no natural enemies, being fully protected both in the larval and pupal stages. Physical remedies are, therefore, necessary, such as the removal of larvae and pupae from their burrows by hand."

The mango shoot psylla (Psylla cistellata Buckton) is reported only from India. "It injures the terminal shoots by producing imbricated pseudo-cones of a bright green or yellow color in which the larval and pupal stages are passed." Dino-derus distinctus is a beetle which attacks branches of the mango in India. Sternochetus gravis is the mango weevil of northern India, similar to the common mango weevil described above. These and many other insects reported as attacking the mango in various parts of the world are described in "A Manual of Dangerous Insects," published by the United States Department of Agriculture (1917). The scale insects are particularly numerous, and cannot be listed here. Several of them are common in the mango orchards of Florida. The genera Aspidiotus, Chionaspis, Coccus, Pulvinaria, and Saissetia are well represented in different parts of the world. Generally speaking, their control by spraying is relatively simple.